1. Field of the Invention
The present invention relates to a router and a communication network system, and in particular to a router and a communication network system reserving network resources in compliance with an RSVP (Resource ReSerVation Protocol), that is a protocol for resource reservation.
2. Description of the Related Art
Application Examples of RSVP
In the RSVP, each router transferring packets between a first and a second host makes a reservation (resource reservation) of quality of service (QoS) provided.
FIG. 24 shows an example of a general resource reservation by the RSVP. In this example, a communication network NW is composed of routers R1-R3 and a home agent HA, and a first host CN is connected to the router R1. It is to be noted that the home agent HA is a router as well.
Also, a mobile node MN is a terminal having an address used in a home link HL, which can move to a foreign link FL1 managed by the router R2 or to a foreign link FL2 managed by the router R3 in addition to a home link HL managed by the home agent HA.
In the example shown, the mobile node MN is located in the home link HL, while the router R1 and the home agent HA transfer a packet addressed to the mobile node MN from a corresponding node CN.
Hereinafter, the procedure by which the corresponding node CN in this state makes a resource reservation in compliance with the RSVP before transmitting an ordinary packet will be described.    (1) The corresponding node CN transmits to the mobile node MN a path message PM1 having set therein an address of the node itself as an RSVP_HOP (occasionally referred to as PHOP since IP address of Previous HOP (PHOP) is generally used). The router R1 having received the path message PM1 holds the information therein as a path state.
As contents of a general path state, session information (destination address (DestAddress), a protocol ID (Protocol_ID), a destination port number (DestPort)), the RSVP_HOP, and the like are used. As a path state in the router R1 shown, the PHOP is the address of the corresponding node CN, and the destination is the home address of the mobile node MN.
The router R1 sets the address of its own in the PHOP of the path message PM1 to be transferred as a path message PM2 to the mobile node MN.    (2) The home agent HA having received the path message PM2 generates and holds a path state based thereon in which the PHOP is the address of the router R1 and the destination is the home address of the mobile node MN.
Moreover, the home agent HA sets the address of its own in the PHOP of the path message PM2 to be transferred as a path message PM3 to the mobile node MN.    (3) The mobile node MN having received the path message PM3 generates and holds a path state based thereon in which the PHOP is the address of the home agent HA and the destination is the home address of the mobile node MN, and transmits a reservation message RM1 in response to the path message PM3.
It is to be noted that the destination of the reservation message RM1 is the PHOP stored in the path message PM3.    (4) The home agent HA having received the reservation message RM1 holds the information of the reservation message RM1 as a reservation state, so that a service quality upon transferring a packet transmitted from the corresponding node CN can be provided. It is to be noted that the reservation state includes session information, resource reservation information, and the like.
Moreover, the home agent HA transmits a reservation message RM2 to the address of the router R1 that is the PHOP of the path state held.    (5) The router R1 having received the reservation message RM2 holds the information of the reservation message RM2 as a reservation state, and further transmits a reservation message RM3 addressed to the corresponding node CN that is the PHOP of the path state held.
By the above-mentioned procedures (1)-(5), the resource reservation is made for all of the routers supporting the RSVP between the corresponding node CN and the mobile node MN, namely, the router R1 and the home agent HA in this case. It is to be noted that the corresponding node CN can recognize that the resource reservation has been completed by receiving the reservation message RM3.
Various Forms of Encapsulation-and-transfer
Meanwhile, examples of using a technology of an encapsulation-and-transfer in the communication network will be described hereinafter.
(A) Encapsulation-and-transfer in General Mobile IP
In a general mobile IP, when the mobile node MN moves from the home link HL, the home agent HA generates an entry associating the mobile node MN with its care-of address (hereinafter, occasionally abbreviated as CoA) in a binding cache, so that a packet addressed to the mobile node MN arriving thereafter from the corresponding node CN is encapsulated and transferred (hereinafter, simply and occasionally referred to as “encapsulated”) to the care-of address.
Also, when the link in which the mobile node MN is located is changed by moving, the mobile node MN receives a new router advertisement from the connected router, so that a new care-of address is generated again.
Thereafter, the mobile node MN notifies the change of the care-of address to the home agent HA using a binding update message. Upon receiving the binding update, the home agent HA updates the corresponding entry of the binding cache, so that the packet addressed to the mobile node MN from the corresponding node CN arriving thereafter is encapsulated to the new care-of address.
In a communication network having applied thereto such a general mobile IP, an example where the home agent HA encapsulates a packet destined for the home address of the mobile node MN with the care-of address of the mobile node MN to be transferred will be described referring to FIG. 25. The arrangement of FIG. 25 is the same as that of FIG. 24, except that FIG. 25 shows a state where the mobile node MN has moved to the foreign link FL1 managed by the router R2.    (1) Firstly, the corresponding node CN transmits a packet M1 to the mobile node MN. In this case, the corresponding node CN knows only the home address of the mobile node MN, so that the destination of the packet M1 indicates the home address of the mobile node MN.    (2) When the packet M1 reaches the home agent HA through the router R1, the home agent HA retrieves the binding cache, reads the care-of address (CoA) of the mobile node MN, and encapsulates the packet M1 with the care-of address as the destination, to be transferred as a packet M2.    (3) When the encapsulated packet M2 reaches the mobile node MN through the router R2, the mobile node MN takes out the original packet M1 by decapsulating the packet M2.(B) Encapsulation-and-transfer in Hierarchical Mobile IP System
In contrast to the above-mentioned general mobile IP, there is a hierarchical mobile IP system (described as “Hierarchical MIPv6” in the IETF draft “draft-ietf-mobileip-hmipv6-04.txt”) in which a mobility agent MA equivalent to an agent for the home agent HA is provided aside from the home agent HA, whereby the movement of the mobile node MN within the network managed by the mobility agent MA is concealed from the home agent HA.
FIG. 26 shows such a hierarchical mobile IP system, having an arrangement where the mobility agent MA is added to the arrangement of FIG. 25.
In such a hierarchical mobile IP system, the binding cache of the home agent HA associates the home address of the mobile node MN with a virtual care-of address (VCoA) under the mobility agent MA.
Also, the mobility agent MA associates the home address of the mobile node MN with a physical care-of address (PCoA) under the router where the mobile node MN is actually located, e.g. the router R2.
In this case, the mobile node MN transmits the binding update not to the home agent HA but to the mobility agent MA as far as the movement is within the network managed by the mobility agent MA.
Thus, it seems to the home agent HA as if the mobile node MN is located under the mobility agent MA.
Hereinafter, the encapsulation-and-transfer in such a hierarchical mobile IP system will be described referring to FIG. 26.    (1) The corresponding node CN transmits a packet M1 to the mobile node MN.    (2) When the packet M1 reaches the home agent HA through the router R1, the home agent HA retrieves the binding cache, reads the virtual care-of address (VCoA) of the mobile node MN, and encapsulates the packet M1 with the care-of address as the destination, to be transferred as a packet M2.    (3) The mobility agent MA having received the encapsulated packet M2 encapsulates it again, or re-encapsulates it, destined for the physical care-of address (PCoA) in the network to which the mobile node MN has moved, to be transferred as a packet M3.    (4) The mobile node MN having received the encapsulated packet M3 destined for the PCoA through the router R2 takes out the original packet M1 by decapsulation.(C) Mobile IP System Using Edge Node
Hereinafter, a mobile IP system using an edge node will be described referring to FIG. 27 in which a virtual home agent VHA and an edge node EN are respectively substituted for the home agent HA and the router R1 in FIG. 24.
In this case, the edge node EN provided in a position nearer to the corresponding node CN than the virtual home agent VHA copies the binding cache of the virtual home agent VHA upon arrival of the packet, retrieves the binding cache instead of the virtual home agent VHA, and performs the encapsulation processing, thereby optimizing a transferring route within the network.
Also, the virtual home agent VHA (occasionally referred to as a temporary home agent (THA) when applied to the above-mentioned hierarchical mobile IP) has a function of the home agent HA and a function of delivering the binding cache to the edge node EN.
Hereinafter, an example of the encapsulation-and-transfer in the mobile IP system using the edge node will be described referring to FIG. 27.    (1) The corresponding node CN transmits a packet M1 to the mobile node MN.    (2) When the packet M1 reaches the virtual home agent VHA through the edge node EN, the virtual home agent VHA retrieves the binding cache, reads the care-of address (CoA) of the mobile node MN, and encapsulates the packet M1 with the care-of address as the destination, to be transferred as a packet M2.    (3) The encapsulated packet M2 reaches the mobile node MN through the router R2.    (4) The edge node EN having transferred the packet M1 in the above-mentioned (1) transmits a cache request C1 addressed to the transferring destination, i.e. the home address of the mobile node MN.    (5) The virtual home agent VHA having received the cache request C1 returns a binding cache associated with the mobile node MN by a cache notification C2 to the edge node EN, in the presence of a binding cache corresponding to the destination.    (6) The edge node EN having received the cache notification C2 generates and holds a binding cache associated with the home address of the mobile node MN.    (7) Hereafter, the corresponding node CN transmits a packet M3 to the home address of the mobile node MN.    (8) The edge node EN refers to the binding cache, and encapsulates the packet destined for the home address of the mobile node MN with the care-of address CoA as the destination, to be transferred as a packet M4.    (9) The mobile node MN having received the encapsulated packet M4 destined for the PCoA through the router R2 takes out the original packet M3 by decapsulation.(D) Encapsulation-and-transfer in IP-VPN
Apart from the communication network using mobile IP in the above-mentioned (A)-(C), the encapsulation-and-transfer is performed in an IP-VPN (Internet Protocol-Virtual Private Network), that is a virtual private network service restricting the transmission protocol to the IP.
FIGS. 28A and 28B show an example of the IP-VPN using a tunnel mode of an IPsec (IP security). As shown in FIG. 28A, terminals CN1-CN3 and MN1-MN3 are respectively connected to gateways GW1 and GW2. The gateways GW1 and GW2 respectively have stored therein encapsulation tables TBL1 and TBL2 to be referred upon an encapsulation.
Also, an encapsulation-and-transfer section between the gateways GW1 and GW2 is composed of e.g. routers R1-R6 as shown in FIG. 28B. It is to be noted that the routers R1 and R2 are the gateway routers respectively corresponding to the gateways GW1 and GW2, so that in the following explanation, the gateways GW1 and GW2 are occasionally represented by the routers R1 and R2.
In such an IP-VPN, e.g. a packet transmitted from the terminal CN1 to the terminal MN1 is encapsulated at the gateway GW1. At this time, the gateway GW1 (router R1) refers to the encapsulation table TBL1 in which the destination address and an encapsulated destination are associated with each other as shown in FIG. 29, and encapsulates the packet addressed to the terminal MN1 with the destination of the router R2, to be transferred.
The encapsulated packet has, for example, a packet format of the tunnel mode of the IPsec as shown in FIG. 30. An encryption region of the packet format shown in FIG. 30 is a region where an ESP trailer is added to an original IP header, an original expanded header, a TCP header, and data composing the packet before the encapsulation.
An ESP header and ESP authentication data are added to this encryption region, and a new expanded header and a new IP header are further added thereto.
The gateway GW2 (router R2) recovers the original packet by decapsulating the received packet, to be transmitted to the terminal MN1.
The first problem when making the resource reservation in compliance with the RSVP is that when the encapsulated transfer of the packet is performed as in the above-mentioned (A)-(D), the path message transmitted when making the resource reservation in compliance with the RSVP is also encapsulated.
FIG. 31 shows a case supposing that the corresponding node CN makes a resource reservation in a state where the mobile node MN has moved to the foreign link FL1 in the same way as in FIG. 25.
In this case, the operations of the corresponding node CN, the router R1, the home agent HA, and the mobile node MN are the same as those of FIG. 24, except that in FIG. 31, the path message PM3 transferred by the home agent HA to the mobile node MN is encapsulated through the router R2 since the mobile node MN has moved to the foreign link FL1.
The encapsulated path message PM3 can be decapsulated only by the mobile node MN which is the destination, so that the router R2 on the way treats the path message PM3 as an ordinary packet. Namely, a path state is not generated by the router R2. Therefore, the router R2 does not generate a reservation state when transferring the reservation message RM1 from the mobile node MN to the home agent HA.
Thus, in FIG. 31, the resource reservation can be made in the router R1 and in the home agent HA, but can not be made in the router R2. However, the corresponding node CN receives the reservation message RM3 in the same way as in FIG. 24. Therefore, although it seems as if the resource reservation is completed, as a matter of fact, the operation will be continued by a service quality different from what was requested.
Similar problems arise in the hierarchical mobile IP system shown in FIG. 26, and in the mobile IP using the edge node shown in FIG. 27.
Also, as shown in FIG. 32, when the resource reservation is made between the transmitting terminal CN1 and the second host MN1 in the IP-VPN, the resource reservation is made by the path messages PM1-PM3 and the reservation messages RM1-RM3 as follows:    (1) The path message PM1 from the transmitting terminal CN1 is encapsulated by the router R1, to be encapsulated as a path message PM2 to the router R2. At this time, the router R1 generates and holds a path state wherein the PHOP is the address of the transmitting terminal CN1, and the destination is the address of the second host MN1.    (2) The router R2 having received the path message PM2 through the routers R4 and R3 decapsulates the path message PM2. While transmitting the path message PM3 to the second host MN1, the router R2 generates and holds a path state wherein the PHOP is the address of the router R1, and the destination is the address of the second host MN1.    (3) When the second host MN1 transmits a reservation message RM1 in response to the path message PM3, the router R2 having received the reservation message RM1 generates and holds a reservation state wherein the destination is the address of the second host. Also, the reservation message RM1 is encapsulated as the reservation message RM2 addressed to the router R1.    (4) The router R1 having received the reservation message RM2 through the routers R3 and R4 decapsulates the reservation message RM2. While transmitting a reservation message RM3 to the transmitting terminal CN1, the router R1 generates and holds a reservation state wherein the destination is the address of the second host MN1.
Thus, the routers R1 and R2 hold the path states and reservation states, so that the resource reservation is made. However, the routers R3 and R4 transferring the encapsulated path message PM2 and the reservation message RM2 do not make the resource reservation.
Specifically, when the path message PM2 and the reservation message RM2 are encrypted packets as shown in FIG. 30, the routers R3 and R4 on the way can not make the resource reservation since the determination or the decoding of the message is not possible.
The second problem in making the resource reservation in compliance with the RSVP is that in a mobile communication system, even if a normal resource reservation is made, when the mobile node MN moves, the communication will be continued without making a resource reservation between the home agent and the moving destination of the mobile node MN.
Such an example will be described referring to FIG. 33. FIG. 33 shows a case similar to FIG. 24 in which the mobile node MN moves to the foreign link FL1 after the completion of the resource reservation by the path messages PM1-PM3 and the reservation messages RM1-RM3 in the state where the mobile node MN has been located in the home link HL.
In this case, the router R1 holds a path state in which the PHOP is the address of the corresponding node CN and the destination is the home address of the mobile node MN as shown by (1) in FIG. 33, as well as a reservation state in which the destination is the home address of the mobile node as shown by (5) in FIG. 33.
Also, the home agent HA holds a path state in which the PHOP is the address of the router R1 and the destination is the home address of the mobile node MN as shown by (2) in FIG. 33, as well as a reservation state in which the destination is the home address of the mobile node MN as shown by (4) in FIG. 33.
Furthermore, while being located in the home link HL, the mobile node MN holds a path state in which the PHOP is the address of the home agent and the destination is the home address of the mobile node MN as shown by (3) in FIG. 33.
When the mobile node MN moves to the foreign link FL1 in such a state, a packet M1 transmitted thereafter from the corresponding node CN to the mobile node MN reaches the mobile node MN as a packet M2 having encapsulated by the home agent HA.
In this case, the resource reservation is not made in the router R2, so that the service by the requested service quality is not provided. Also, although the router R1 having made the resource reservation in advance provides the service, there is a problem that the home agent HA does not provide the service since the destination of the encapsulation-and-transfer at the home agent HA assumes the care-of address of the mobile node MN which is different from the home address of the mobile node MN, that is the address when the resource reservation was made.